Imaging apparatus and zoom control method

1. An imaging apparatus comprising: an imaging unit configured to capture a video of a subject image through a lens barrel; an instruction unit configured to instruct a trigger of focusing of a lens before a recording of the video starts; an optical zoom unit configured to move at least a portion of lenses that are included in the lens barrel and to change an angular field of the subject image that can be captured by the imaging unit; an electronic zoom unit configured to change a photographic range of a photographic image that has been obtained by the imaging unit by image processing; an obtaining unit configured to obtain a focal distance of a lens and a distance to a subject; a depth of field calculating unit configured to calculate a depth of field of a subject image that has been obtained through the lens barrel, wherein the depth of field calculating unit calculates the depth of field of the subject image after a focusing operation has been carried out based on the trigger of the focusing instructed by the instruction unit and after the recording of the video has started, and wherein the depth of field calculating unit calculates the depth of field of the subject image based on the focal distance of the lens and the distance to the subject obtained by the obtaining unit; and a control unit configured to switch between the optical zoom unit and the electronic zoom unit according to the depth of field that has been calculated by the depth of field calculating unit.

2. The imaging apparatus according to claim 1 , wherein the control unit switches to using the electronic zoom unit in a zoom region in which the depth of field that has been calculated by the depth of field calculating unit is shallower than a preset depth of field.

3. The imaging apparatus according to claim 1 , further comprising a photography conditions setting unit configured to set photography conditions, including at least a setting for an aperture value of the lens barrel, wherein the photography conditions setting unit carries out depth of field priority mode that sets the photography conditions such that the depth of field is deep.

4. The imaging apparatus according to claim 1 , wherein the lens barrel is an interchangeable lens that is freely detachable from the imaging apparatus.

5. The imaging apparatus according to claim 1 , wherein the control unit switches between the optical zoom unit and the electronic zoom unit according to whether or not the depth of field is shallower than a specified value.

6. A zoom control method for an imaging apparatus comprising: capturing, by an imaging unit, a video of a subject image through a lens barrel; instructing, by an instruction unit, a trigger of focusing of a lens before a recording of the video starts; moving, by an optical zoom unit, at least a portion of lenses that are included in the lens barrel and changing an angular field of the subject image that can be captured by the imaging unit; changing, by an electronic zoom unit, a photographic range of a photographic image that has been obtained by the imaging unit; obtaining, by an obtaining unit, a focal distance of the lens and a distance to a subject; calculating, by a depth of field calculating unit, a depth of field of a subject image that has been obtained through the lens barrel, wherein the depth of field calculating unit calculates the depth of field of the subject image after the focusing operation has been carried out based on the trigger of the focusing instructed by the instruction unit and after the recording of the video has started, and wherein the depth of field calculating unit calculates the depth of field of the subject image based on the focal distance of the lens and the distance to the subject obtained by the obtaining unit; and switching, by a control unit, between the optical zoom unit and the electronic zoom unit according to the depth of field that has been calculated by the depth of field calculating unit.